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In this study, we revealed how the petals of Saintpaulia fuse into a corolla by using pinwheel phenotype cultivars. Striped patterns in petal, called pinwheel in Saintpaulia, are attractive phenotypes and thought to be the result of periclinal chimerism. For the selection of a genuine periclinal chimeric cultivar from three pinwheel cultivars, adventitious shoots were induced from leaf lamina. Shoot regeneration was observed from the epidermis in all cultivars by microscopic observation. All regenerated shoots from ‘Kaname’ flowered as monochromatic pink flowers, corresponding to an L1 phenotype of the cultivar. From the other two cultivars, many shoots flowered not only as an epidermal phenotype but also as a phenotype of the inner layer. In addition, shoot regeneration was induced from epidermis-peeled petioles from these three cultivars. All shoots from ‘Kaname’ flowered as monochromatic blue flowers, corresponding to an L2 phenotype. On the other hand, many shoots from ‘Kilauea’ flowered not only as monochromatic flowers, corresponding to an L2 phenotype, but also as bi-colored flowers. ‘Innocent Pink’ did not produce shoots from epidermal-peeled petioles. These results suggested that ‘Kaname’ is a genuine periclinal chimera, while the other two cultivars have other mechanisms for pinwheel expression. Genomic PCR using primers that amplifies almost the full length of flavonoid 3′,5′-hydroxylase (F3ʹ5ʹH) revealed the gene to be non-functional in pink flowers from L1 of ‘Kaname’. From monochromatic pink plants and pink portions of the corolla of ‘Kaname’, full-length F3ʹ5ʹH was not amplified. Similar results were obtained by quantitative PCR. Finally, we observed the fused portion of the petals and revealed that the petal fusion did not occur by postgenital fusion but by “connection”. The process, in Saintpaulia, comprises periclinal cell division in L1 during petal development, active cell division at the edge of the petal, adhesion to the next petals, and fusion. These steps create a striped flower color in Saintpaulia.

African violet (Saintpaulia ionantha H. Wendl.) (Gesneriaceae) is a popular ornamental pot plant that is easy to culture ex vitro and in vitro relative to other herbaceous ornamentals. This quality makes it an ideal system for in vitro regeneration experiments. This review summarizes the studies that have been conducted on the in vitro culture and micropropagation of this plant. Although shoot regeneration from internodes, floral buds, anthers and protoplasts has been achieved, leaf blades and petioles have been a popular source tissue for regeneration. An effective and reproducible protocol for the direct induction of shoots, without the formation of any intermediary callus, involves the use of a cytokinin like BA or kinetin, usually in combination with an auxin like NAA, both within a concentration range of 0.1 to 1 mg/L, and on a Murashige and Skoog basal medium. Shoots can form in both light and darkness, but most effectively in the light, and rooting can be induced from shoots, even in the absence of an auxin, although a low concentration (0.1–0.5 mg/L) of NAA or IAA is recommended. African violets acclimatize easily, even in a simple soil-based substrate, and can flower within 4 months of transfer to ex vitro conditions. These protocols, including somatic embryogenesis and cryopreservation, may also benefit the in vitro culture and conservation of wild species of Saintpaulia.

The color of African violet flowers (Saintpaulia ionantha Wendl.) is derived from anthocyanin pigments. A mutation in the L1 layer of the SAM suppresses the anthocyanin biosynthesis pathway and eventually generates a pinwheel phenotype of periclinal chimera (cells of different genotypes). The aim of the present research was to understand the coloration pathway of petals and how color changes with phenotype. Flower development was investigated by light and scanning electron microscopy (SEM). Expression of nine genes involved in anthocyanin biosynthesis pathway in monochromatic and pinwheel phenotypes were evaluated by Real-Time PCR. Anthocyanin present in pinwheel petals was analyzed by HPLC. Microscopic studies revealed that the ventral petals were formed before the dorsal petals and that the petal primordia separated in the early stages of floral development. Saintpaulia flower is protandry and the tapetum layer is of the secretory type. The ovules are anatropous and are within the superior ovary with lateral placentation. Gene expression analysis showed that CHS and CHI genes were expressed at all stages of floral development, but hydroxylase genes increased during intermediate stages. Biosynthetic genes were highly expressed in the purple sections of the pinwheel petals, whereas the expression of F3H gene was significantly lower in the white section. The WDR transcription factor appears to have no association with the anthocyanin biosynthesis pathway genes in the white section. HPLC analysis showed that when F3H gene expression was reduced in the white part of the petals, the product of this gene (dihydrokaempferol component) did not accumulate. Color change is one of the most effective methods to create new cultivars. Details of floral pigment biosynthesis pathway and the production of new cultivars can respond to consumer demand and market preservation.

Within the family Gesneriaceae, the two related genera Saintpaulia and Streptocarpus contain species that are used as ornamental potted plants. Crosses within the genus Streptocarpus subgenus Streptocarpella and between Streptocarpus and Saintpaulia ionantha were carried out to produce new ornamental plants. Crossing barriers were localised, and methods to overcome these barriers were tested. The in vitro germination ability of pollen was determined; germination varied from 3 to 85% among genotypes. A high correlation coefficient of 0.99 was found between the assessment of pollen viability using staining with 2,5-diphenyl tetrazolium bromide (MTT) and in vitro germination. From crosses of nine Streptocarpus species from the subgenus Streptocarpella, 11 hybrids were established. Hybridity was confirmed in five of these crosses by morphological and RAPD (random amplified polymorphic DNA) marker analysis. An embryo rescue technique was used in an attempt to overcome existing post-zygotic barriers in intergeneric crosses between S. ionantha and Streptocarpus species. Despite swelling of the ovules, which is usually considered as an indicator for successful fertilisation, no germination of plants from embryos was observed with this method.

The effects of 960 MeV carbon ion beam and 8 MeV X-ray irradiation on adventitious shoots from in vitro leaf explants of two different Saintpaulia ionahta (Mauve and Indikon) cultivars were studied with regard to tissue increase, shoots differentiation and morphology changes in the shoots. The experimental results showed that the survival fraction of shoot formation for the Mauve and Indikon irradiated with the carbon ion beam at 20 Gy were 0.715 and 0.600, respectively, while those for both the cultivars exposed to the X-ray irradiation at the same dose were 1.000. Relative biological effectiveness (RBE) of Mauve with respect to X-ray was about two. Secondly, the percentage of regenerating explants with malformed shoots in all Mauve regenerating explants irradiated with carbon ion beam at 20 Gy accounted for 49.6%, while that irradiated with the same dose of X-ray irradiation was only 4.7%; as for Saintpaulia ionahta Indikon irradiated with 20 Gy carbon ion beam, the percentage was 43.3%, which was higher than that of X-ray irradiation. Last, many chlorophyll deficient and other varieties of mutants were obtained in this study. Based on the results above, it can be concluded that the effect of mutation induction by carbon ion beam irradiation on the leaf explants of Saintpaulia ionahta is better than that by X-ray irradiation; and the optimal mutagenic dose varies from 20 Gy to 25 Gy for carbon ion beam irradiation.

The relationship between the susceptibility to rapid temperature drop induced leaf injury, i.e. “leaf spot”, and the antioxidant capacities of several Saintpaulia (African violet) cultivars was examined. Cultivars ‘Ritali’ and ‘Tamiko’, that are more susceptible to leaf spot caused by a rapid drop in leaf temperature from 30 to 15°C than are cultivars ‘Maui’ and ‘New Jersey’. The susceptible cultivars were also more susceptible to oxidative stress caused by H2O2 and active chlorine than the tolerant cultivars. Reduction of available chlorine, considered to be accelerated by antioxidants of leaf tissue, was rapid in ‘Maui’ and ‘New Jersey’. Activity of the antioxidant enzymes superoxide dismutase and catalase were higher in the leaves of ‘Maui’ and ‘New Jersey’ than in the susceptible cultivars. These findings show a correlation between leaf spot injury and antioxidant capacity in Saintpaulia leaves.

Erwinia chrysanthemi spp. are Gram-negative bacterial phytopathogens causing soft rots in a number of plants. The structure of the extracellular polysaccharide (EPS) produced by the E. chrysanthemi strain A350, which is a lac Z − mutant of the wild type strain 3937, pathogenic to Saintpaulia, has been determined using a combination of chemical and physical techniques including methylation analysis, low-pressure gel-filtration and anion-exchange chromatography, high-pH anion-exchange chromatography, partial acid hydrolysis, mass spectrometry and 1- and 2D NMR spectroscopy. In contrast to the structures of the EPS reported for other strains of E. chrysanthemi , the EPS from strain A350 contains d -GalA, together with l -Rha p and d -Gal p in a 1:4:1 ratio. Evidence is presented for the following hexasaccharide repeat unit: Download full-size image All the Erwinia chrysanthemi spp. studied to date have been analyzed by ribotyping and collated into families, which are consistent with the related structures of their EPS.

Summary A synopsis of the poorly known genus Linnaeopsis , endemic to the Uluguru Mts. in Tanzania, is provided. Three species are recognized: L. subscandens B. L. B urtt , L. heckmanniana E ngl . and L. alba (E. A. B ruce ) B. L. B urtt . L. heckmanniana is subdivided into two subspecies, ssp. heckmanniana and ssp. gracilis (E. A. B ruce ) W eigend , stat. nov., and also in L. alba two subspecies are distinguished, ssp. alba and ssp. edwardsii W eigend , subsp. nov. The latter is marked by rugose leaves with 5-to 6-celled trichomes on the adaxial side (vs. 3- to 4-celled hairs in ssp. alba ) and by different hair cover of the ovary and stem. The affinities of Linnaeopsis are discussed and an origin within or near Streptocarpus subg. Streptocarpus suggested. A close relationship with Saintpaulia appears rather unlikely.

The change in chlorophyll fluorescence was investigated using fluorescence microscopy at the initial stage of leaf spot occurrence in Saintpaulia ionantha H. Wendl. (African violet). When Saintpaulia leaf was exposed to a rapid temperature drop, fluorescence intensity declined very quickly within a very short time (20 s) and did not recover after rewarming. This abrupt reduction of chlorophyll fluorescence was caused even by 20°C water for just 2 s, when leaf temperature prior to treatment was 35°C. This change of chlorophyll fluorescence was observed only in the palisade cells in a leaf. In addition, ultrastructural study of the chloroplast of the palisade cells showed an abrupt disruption in the photosynthetic apparatus. These results indicate that the initial stage of leaf spot occurrence is developed very quickly within a very short time and that it might be caused by a different mechanism to conventional chilling injury.

Shoot organogenesis in African Violet was affected by factors including leaf age, wounding and leaf disc orientation. A gradient of regenerative potential was found among individual leaves on a plant. This regenerative potential was not directly proportional to the juvenility of leaf tissues. Wound treatment increased shoot organogenesis only when the wound was in direct contact with the medium, possibly by increasing nutrient and hormone uptake. Leaf disc orientation did not affect shoot number per disc but did determine the position of shoot organogenesis. Reduced gas exchange significantly reduced shoot production. This study also showed that adventitious roots originated from spongy mesophyll cells.

Yellow or brown spots (‘leaf spot’) often occur on Saintpaulia ( S. ionantha Wendl cv. Ritali) leaves. Leaf spot has been known to be caused by a rapid temperature drop created overhead irrigation. The sensitivity of Saintpaulia leaves to a temperature drop was investigated at intervals during the day/night cycle. In both a plastic house and a growth chamber, leaf spot sensitivity was highest during the dark period and decreased rapidly from the beginning of a light period, leading to the lowest level 4 h later. Leaf spot sensitivity was greatly influenced by environmental factors such as light, temperature, and humidity, among which light was the most important factor. After a dark period of 12 h, light reduced the sensitivity greatly within 4 h of exposure, and the resumption of dark conditions brought a large increase in the sensitivity within 2 h.

Begonia × elatior plantlets, regenerated from leaf disk callus, showed differences in flower morphology, flower size, plant height, plant morphology and number of flowers per plant. Similarly, a range of somaclonal variation was observed in plantlets regenerated from leaf disks of Saintpaulia ionantha L., without being preceded by the callus phase. Flowering varied from 78 to 109 days. The corolla was tubular in 4% of regenerants and abscissed when touched gently. Non-flowering regenerants had thick and hard leaves. Some had variegated and serrated leaves. Somaclonal variation was recorded in the number of flowers per plant, flower size and the number of petals per flower. Flower color was stable in both species. Micropropagation of two MV1 somaclones of each experimental plant, selected for their desirable traits, stabilized in the MV2 and MV3 generations. The selection of desirable somaclones and their micropropagation in subsequent generations can lead to the development of new and stable lines.

A homogenization technique was developed for the multiplication of Saintpaulia ionantha . Petals from unopened flower buds were used as initial explants, which were homogenized with a blender in distilled water after the formation of adventitious shoots. The homogenate was plated on solidified Murashige and Skoog (MS) medium where it formed clumps with multiple shoots. The effect of benzylaminopurine and α-naphthalene acetic acid, in the initial and plating media, on shoot production was studied. Five commercial cultivars tested were easily multiplied, transferred to soil and grown to flowering plants. The frequencies of ‘off-type’ plants observed were between 0 and 4%.

Five ornamental species grew as well in media that included composted bagasse as those grown in peat moss or pine bark. Plants of most of the species grown in a potting mix which included fresh bagasse grew at reduced rates and the medium shrank excessively. For some species, a medium containing both bark and bagasse may increase production compared with media containing either bark or bagasse alone. Boron (0.1 g l −1 ) applied at fortnightly intervals reduced dry matter production in all species. Media mixed in a commercial mixer (5 m 3 ) had similar effects on plant dry weight to those mixed with a small mixer (0.05 m 3 ). African violets ( Saintpaulia sp.) grew well in a range of media, but produced greater root dry matter in a mix containing a high proportion of composed bagasse.

The Fantasy mutation in Saintpaulia ionantha produced flowers that had a purple background color with pink sectors. The purple background tissue contained kaempferol 3- O -glucoside and malvidin 3-rutinoside-5-glucoside. The pink sector tissue contained kaempferol 3- O -glucoside and peonidin-3-rutinoside-5-glucoside.

Details of common media and procedures are given for the regeneration of plants from disks of mature leaves and young axenic leaves of African Violet. Growth analysis of the progeny plant populations show differences in plant diameter, leaf number, leaf area and petiole length between tissue culture progenies and those derived from leaf cuttings. Both the tissue culture progeny poulations had similar character means. Intra-population variation was high for all three progeny populations. Leaf shape, number of flowering plants, number of peduncles and number of flowers and flower buds per plant did not vary among the three progeny populations, but intrapopulation variation was high in the latter characteristic.

Variation in morphogenetic response was observed when leaf disks of 20 randomly selected cultivars of Saintpaulia ionantha Wendl, were cultured on a medium developed for the cultivar ‘Rose’. To eliminate possible variation due to differences in the physiological state of the explants prior to culture, young axenic leaves were taken from 10 of the cultivars. These were placed on factorial media containing either no hormone or various combinations of naphthalene acetic acid and benzylaminopurine. The results of axenic leaf culture showed wide variation, both qualitatively and quantitatively, in the morphogenetic potential of the cultivars. These results are discussed in the context of developing standardized propagation procedures for Saintpaulia ionantha cultivars.

Sport emergences during vegetative propagation of edged and Geneva-edged types of saintpaulia cultivars were observed when compared with centred-type cultivars. According to the frequency and the definite trend in this sport emergence, they are considered as periclinal chimeras. The mechanism of persisting chimeric structures during vegetative propagation is discussed in relation to the origin of adventitious shoots.

Several species of the genus Saintpaulia, popularly known as Usambara violets, have become a remarkable success as indoor plants in Europe and the USA. Their ancestors, some twenty species in total, live in mountains and near the coast in Tanzania and Kenya. The Saintpaulias require a very special environment since they are sensitive to drought and to competition from other plants. Thus, most species live on steep rock surfaces in dense shade where few other plants thrive. The Usambara violets in cultivation are mostly referred to as Saintpaulia ionantha. Previous records of this species refere to a restricted area near Tanga in Tanzania where today it is very rare because of changes in the environment. Tree-felling to create farmland or to obtain firewood has exposed the previously shaded limestone cliffs, making them unsuitable as habitat for Saintpaulia ionantha. Generally speaking, disturbance of the environment by clearance of trees and bushes is the main threat to the survival of most species, particularly those which occur in the lowlands.

Leaves of Saintpaulia irradiated with a small dose of radiation (predose) 24 hr prior to a challenging dose are less sensitive to the challenging dose than un-pretreated leaves. A comparison has been made between the effect of this pre-dose at the plant production level and also at the cellular using a morphological-cytological technique which allows for a determination of the percentage of epidermal cells which regenerate and pass through the first mitosis. Plant production effects are closely paralleled by the effects at the cellular level and an analysis of the cellular effects has indicated that the pre-dose renders the stationary epidermal cells more able to repair potentially lethal damage. The effect of the pre-dose stimulated repair on the induction of mutations in the plantlets derived as adventitious shoots from the irradiated leaves has been studied and it is concluded that the stimulated repair tends to be error-free, although not completely.

Summary In six experiments the effect of endogenous factors on the level of free proline in Saintpaulia and Chrysanthemum was investigated. Data showed a significant influence of plant and leaf age and of leaf region in Saintpaulia . Young plants showed the highest proline contents. The results of the leaf age study were unequivocal and seem to be dependent on plant age and cultivar, respectively. A clear concentration gradient of proline was seen within the leaf blades, with the maximal amounts on the edges and the top. In Chrysanthemum , the influence of leaf age on the levels of proline was more clearly evident. Samples collected showed a 96% decrease in the proline content in the range from the 5th leaf down to the 32nd leaf.

Summary The in vitro culture of Saintpaulia petiole cross-sections on a solid medium containing relatively high levels of auxin, produced callus cells with thin walls. Slight teasing of the callus tissue with dissecting needles released high yields of small densely cytoplasmic protoplasts which were stable in the osmotic pressure of standard tissue culture media. This resulting non-enzymatic protoplast isolation method is dependent on the auxin 2,4-dichlorophenoxyacetic acid which partially inhibits cell wall synthesis without preventing cytokinesis in proliferating Saintpaulia callus stock tissue, and suggests a basic approach which may be applicable to a wide range of plant species. These non-enzymatically isolated Saintpaulia protoplasts provide a suitable experimental system for various physiological studies including assessment of the toxicity of cell wall degrading enzymes.

The germination and growth of Brassica oleraceae var. capitata, Lactuca sativa and Matthiola incana were not significantly affected by replacing peat in their growing-media with sawdust ( Eucalyptus and Tristania ) composted with urea (2.6 kg/m 3 ) and other fertilizers for 6 weeks. Two thirds of the peat in the media could be replaced with sawdust before the germination or growth rates of Papaver orientale or Senecio × hybridus were significantly affected, while half of the peat could be replaced with sawdust before Viola × wittrockiana was significantly affected. The growth rates of Adiantum raddianum, Asplenium nidus, Coleus blumei, Dieffenbachia picta, Nephrolepis elata, Peperomia scandens, Philodendron sellonium × specciosum, Pilea cadleri, Saintpaulia and Schefflera actinophylla in media containing 50–80% composted hardwood sawdust were equivalent to, or significantly better than, growth in media containing an equal percentage of sphagnum peat and receiving the same level of liquid or slow-release fertilizer. Substitution of sphagnum peat with composted sawdust reduced the leaf area and dry weight of Impatiens walleriana , possibly due to a small decrease in the available water in the media. It did not, however, have a significant effect on either their number of flowers or their surface area. The growth of Pilea and Saintpaulia was best where the media contained equal percentages of sawdust and peat than where either was used alone.

Ethylene gas and X rays, alone and in combination, were applied to petioles of Saintpaulia ionantha Wendl. to test their effect on peroxidase activity. Both agents increased peroxidase activity, although ethylene was the most effective. X ray treatment of petioles at five different peroxidase levels showed that as the initial activity of peroxidase increased the effect of a given dose of radiation decreased. Also, high doses, near the lethal limit for the species, were proportionately less effective in inducing peroxidase activity than were lower doses. Polyacrylamide disc electrophoresis showed no change in isozyme patterns with increases in peroxidase activity.

Young plants of 10 different greenhouse species were grown from 24 to 100 days at 55–60, 70–75 or 90–95% relative humidity (RH) in growth rooms. The dry weight increased significantly by increasing RH from the lowest to the highest level in Begonia × hiemalis (47%), Saintpaulia ionantha (17–36%), Euphorbia pulcherrima (31%), Chrysanthemum × morifolium (31%), Nephrolepis exaltata (68%) and Lycopersicon esculentum (20%). The dry weight of Campanula isophylla, Rosa, Cucumis sativa and Lactuca sativa was not affected by RH, while Soleirolia soleirolii was negatively affected. The fresh weights of Cucumis and Lactuca , however, increased with RH in spite of there being no effects on the dry weights. Shoot length increased very considerably by raising the RH in most of the species. The number of leaves was increased by RH in some of the species while not in others. Number of flowers and flower buds significantly increased with RH in Saintpaulia , and time to flowering was reduced with RH in Saintpaulia, Begonia and Campanula .

Two cultivars of Saintpaulia (‘Rhapsody’ Nos. 19 and 49) were subjected to three levels of root-zone temperatures, ranging from 17 to 25°C. High root-zone temperatures accelerated flowering as a result of an enhanced rate of plant growth and a promoted flower development; growth analysis showed an increased LAR, resulting in higher growth rates. The percentage plant dry matter decreased compared to the unheated control. Root-zone heating increased the air temperature around the plant and therefore the leaf temperature and growing-point temperature were also increased. Elevated root-zone temperatures reduced cultivation time by 10–15% without unfavourable effects on plant quality and keepability.

Mutants in each of the pel genes (pelA, pelb, pelC, pelD and pelE) which encode the five pectate lyase isozymes (PLa, PLb, PLc, PLd or PLe) of Erwinia chrysanthemi strain 3937, a pathogen of Saintpaulia ionantha, were obtained by insertion directed mutagenesis. The five mutant strains were tested for pathogenicity by inoculating into mini-saintpaulia plants. The acidic PLa and the basic PLd and PLe isozymes are the most important for pathogenicity. The mutants which were unable to produce the neutral, PLb or PLc, isozymes behaved like the wild type strain and macerated the whole miniplant. In contrast the PelA− and PelD− mutant strains were less virulent than the wild type strain, producing fewer systemically infected plants and much more limited maceration. The PelE− mutant strain was non-invasive, with maceration and bacteria being confined to the one leaf or the part of the leaf blade which was inoculated, suggesting that plant defence reactions had taken place.

Saintpaulia ionantha “Ulery” Wend. cuttings were irradiated with thermal neutrons (250, 1000 and 5000 rad) to determine radiation effects on lethality, root formation, morphology and peroxidase isozymes. Lethality was high at the high doses. Irradiated cuttings showed increases in the time required for roots to form. Although no morphologically distinct mutants were recovered, separation of peroxidase proteins showed that radiation permanently altered peroxidase isozyme patterns. Radiation-induced mutations increased the number of isozymes which were catalytically active but different in their electrophoretic mobility. Radiation also destroyed the catalytic activity or suppressed synthesis of native isozymes. Thus, the isolation of peroxidase isozymes served as an effective genetic marker for radiation-induced mutants.

Plants of three cultivars of Saintpaulia ionantha and Chrysanthemum × morifolium were grown until flowering at 335 (normal) or 900 μl l−1 CO2 (high). Continuous high CO2 concentration increased the final dry weights from 76 to 123% in Saintpaulia and from 15 to 32% in Chrysanthemum compared to the normal concentration. Changing the CO2 concentration from normal to high (intermittent) in intervals of 1 h resulted in dry weights intermediate to that of constant normal or constant high CO2 concentrations in both species. Morning and evening enrichment gave the same effect as 1-h intermittent enrichment in Saintpaulia. High CO2 concentration given every other day gave the same effect as 1 h intermittent CO2 in Chrysanthemum. Increased dry weights were accompanied by more and larger leaves in Saintpaulia, and mainly by thicker and longer stem and more lateral breaks in Chrysanthemum. Time to flowering was significantly reduced by CO2 enrichment in Saintpaulia, but was generally not affected in Chrysanthemum. Number of flowers and flowerbuds was increased by CO2 application in both species. Constant high CO2 concentration generally had effects superior to that of the intermittent treatments.